A semiconductor portion of a super junction n-FET (field effect transistor) includes an n-type drain layer and a drift layer with p-doped columns separated by n-doped columns. In the reverse mode, depletion zones extend between the p-doped and n-doped columns in a lateral direction such that a high reverse breakdown voltage can be achieved even at a high impurity concentration in the n-doped columns. The vertical impurity distribution in the p-doped and/or the n-doped columns may vary with the distance to the drain layer such that device characteristics are improved in case an avalanche effect is triggered. It is desirable to further improve the avalanche characteristics of super junction semiconductor devices without unduly adversely affecting the on-state characteristics.